Younging directions in the Dawros peridotite, Connemara

The syn-D2 Dawros peridotite comprises a sequence of layered harzburgites (associated with massive orthopyroxenites) which pass upwards via a transition marked by the first appearance of chromitite layers into layered lherzolites. Microprobe analyses reveal that the ultramafic sequence exhibits a range in olivine composition from Fo_91.9 to Fo_82.3 and a range in orthopyroxene from En_91.9 to En_{84 3}. A transgressive metagabbro lens in the central outcrop is interpreted as a syn-D2 intrusion into the ultramafic sequence and contains olivine (Fo_{80 4}) and a range in orthopyroxene from En_81.5 to En_76.0. Mg/Fe ratios in coexisting olivines and pyroxenes are used with new structural data to elucidate younging directions in the layered parts of the peridotite. The exposed sequence youngs consistently NE but is repeated by faulting and locally reversed by F4 folding. The peridotite and its immediate hornfels became detached from the surrounding metasediments during D3 and now lie on the SW limb of a recumbent downward facing F3 antiform which plunges NW. Consideration of the structure in adjacent areas suggests that the Dawros and Currywongaun-Doughruagh intrusions lie within a single major F2 fold limb.